This study conducted a survey on flora at Mt. susdolbon(508m), Mt. seongjubong (625.3m), and Mt. sulibong(596.2m), located in Yanggu-gun, Gangwon-do. A total of 403 taxa, including 6 forms, 43 varieties, 4 subspecies, 350 species, 255 genera, and 84 families, were surveyed in the three mountain areas. 18 taxa from 5 families of ferns, 3 taxa from 1 family of gymnosperms, and the dicotyledonous plants as 302 taxa from 69 families of the dicotyledonous plants were identified. The remarkable plants included 11 taxa of the Korean endemic plants, such as Populus tomentiglandulosa, Salix koriyanagi, Cimicifuga heracleifolia, Aconitum pseudolaeve, Clematis trichotoma, Echinosophora koreensis, Vicia chosenensis, Salvia chanryoenica, and Hemerocallis hakuunensis. The rare plants designated by the Korea Forest Service were 4 taxa, including Echinosophora koreensis as endangered species (EC), Cimicifuga heracleifolia, Epimedium koreanum, and Lilium cernuum. The Least Concern species (LC) were 13 taxa, including Persicaria orientalis, Exochorda serratifolia, Viola diamantiaca, Lithospermum erythrorhizon, and Trigonotis icumae. The invasive alien plants were 28 taxa, including Persicaria orientalis, Rumex crispus, Phytolacca americana, Cerastium glomeratum, Chenopodium album, Chenopodium ficifolium, Amorpha fruticosa, Robinia pseudoacacia, Trifolium pratense, Trifolium repens, Oxalis dillenii, Euphorbia supina, and Oenothera biennis, accounting for 6.9 percent of the 403 taxa of the surveyed plants.